It has been found desirable to have locking knobs on electrical instruments so as to prevent inadvertent adjusting once set and to avoid displacement caused by vibrations and the like. The prior art teaches several different devices that accomplish this purpose. Most of these devices are somewhat complicated in construction since they require many components to constitute the locking device. Because of the unnecessary complicated design of the prior locking devices, the assembly of such devices is more costly and time consuming than would be if the device had a minimal amount of components.